Neoplasia occurs when normal body cells are changed, proliferating without regard to normal cellular restraints, and invade and colonize areas of the body normally occupied by other cells. See B. Alberts et al., Molecular Biology of the Cell 1255-1294 (3d ed. 1994). According to the American Cancer Society, one-half of American men and one-third of American women will at some point in their lives develop a neoplastic disorder.
Abnormal cell proliferation is usually characterized by an increase rate of division and in some cases uncontrolled growth. One example of a proliferative cell disorder is a tumor or neoplasm. In addition to posing a serious risk in and of themselves, primary malignant neoplasms are particularly problematic given their tendency to invade surrounding tissues and metastasize to distant organs in the body. To date, the most frequently used methods for treating neoplasia include surgical procedures, radiation therapy, and drug therapies, and combinations of the foregoing. These methods involve significant risk (e.g., of infection, death) to the patient. More importantly, the probability of eliminating all malignant cells is small, particularly if the zone of the malignant growth is not well defined or if the primary tumor has metastasized by the time of surgery. Achieving therapeutic doses effective for treating neoplasm is often limited by the toxic side effects of the anti-cancer agent on normal, healthy tissue. An ideal anti-cancer agent has tissue specificity, thereby reducing side-effects on normal (dividing) cells. There is a need in the art for novel cancer therapeutics which have higher efficacy, specificity, or reduced side effects.